U.S. patent application number 13/988216 was filed with the patent office on 2013-09-19 for fiber preform made from reinforcing fiber bundles and comprising unidirectional fiber tapes, and composite component.
This patent application is currently assigned to TOHO TENAX EUROPE GMBH. The applicant listed for this patent is Frank Oberwahrenbrock, Markus Schneider, Andreas Woginger, Bernd Wohlmann. Invention is credited to Frank Oberwahrenbrock, Markus Schneider, Andreas Woginger, Bernd Wohlmann.
Application Number | 20130244018 13/988216 |
Document ID | / |
Family ID | 43901060 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130244018 |
Kind Code |
A1 |
Wohlmann; Bernd ; et
al. |
September 19, 2013 |
FIBER PREFORM MADE FROM REINFORCING FIBER BUNDLES AND COMPRISING
UNIDIRECTIONAL FIBER TAPES, AND COMPOSITE COMPONENT
Abstract
A fiber preform for producing fiber composite structures, a wall
thereof including a first zone made from reinforcing fiber bundles
having a first resin composition and a second zone made from at
least one fiber tape comprising at least one unidirectionally
directed reinforcing yarn strand having a second resin composition.
The reinforcing fiber bundles in the first zone are oriented in
different spatial directions to each other when viewed in a
direction parallel to the extension of the thickness. Each
reinforcing fiber has a length of from 3 to 50 mm, and contains the
first resin composition in a concentration of from 1 to 10 wt % of
the fiber weight. The wall of the fiber preform has a proportion of
reinforcing fibers of more than 35 vol %, and the second zone forms
a discrete region when viewed in a direction perpendicular to the
thickness extension of the wall.
Inventors: |
Wohlmann; Bernd;
(Dusseldorf, DE) ; Schneider; Markus; (Dusseldorf,
DE) ; Woginger; Andreas; (Mannheim, DE) ;
Oberwahrenbrock; Frank; (Wuppertal, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wohlmann; Bernd
Schneider; Markus
Woginger; Andreas
Oberwahrenbrock; Frank |
Dusseldorf
Dusseldorf
Mannheim
Wuppertal |
|
DE
DE
DE
DE |
|
|
Assignee: |
TOHO TENAX EUROPE GMBH
Wuppertal
DE
|
Family ID: |
43901060 |
Appl. No.: |
13/988216 |
Filed: |
November 11, 2011 |
PCT Filed: |
November 11, 2011 |
PCT NO: |
PCT/EP11/69939 |
371 Date: |
May 17, 2013 |
Current U.S.
Class: |
428/299.7 ;
428/221 |
Current CPC
Class: |
B29C 70/081 20130101;
Y10T 428/24994 20150401; Y10T 428/249921 20150401; B29K 2707/04
20130101; B29B 11/16 20130101; D04H 13/00 20130101; B29C 70/887
20130101; Y10T 428/249947 20150401; Y10T 428/249924 20150401 |
Class at
Publication: |
428/299.7 ;
428/221 |
International
Class: |
D04H 13/00 20060101
D04H013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 2, 2010 |
EP |
10193489.1 |
Claims
1. A fiber preform for producing fiber composite structures, the
fiber preform comprising: a wall made from reinforcing fibers,
wherein: the wall has a first surface, a second surface lying
opposite the first surface and a thickness extending between the
surfaces, and is limited by edges, the wall comprises at least one
first zone made from reinforcing fiber bundles having a first resin
composition and at least one second zone made from at least one
fiber tape comprising at least one unidirectionally directed
reinforcing yarn strand having a second resin composition, the
reinforcing fiber bundles in the at least one first zone are
oriented in differing spatial directions from each other when
viewed in a direction parallel to the thickness extension, each
reinforcing fiber bundle comprises reinforcing fiber filaments
directed parallel to each other, has a length in a range from 3 to
50 mm, and contains the first resin composition in a concentration
in a range from 1 to 10 wt. % relative to the-a fiber weight, the
wall of the fiber preform has a proportion of reinforcing fibers of
greater than 35 vol. %, and the at least one second zone forms a
discrete region when viewed in a direction perpendicular to the
thickness extension of the wall and at least one fiber tape ends
with at least one end thereof inside of the wall.
2. The fiber preform according to claim 1, wherein the wall thereof
comprises at least two fiber tapes and an orientation of the at
least one unidirectionally directed reinforcing yarn strand of at
least one fiber tape is different from an orientation of the at
least one unidirectionally directed reinforcing yarn strand of
another fiber tape.
3. The fiber preform according to claim 1, wherein the at least one
unidirectionally directed reinforcing yarn strand of at least one
fiber tape is not directed parallel to any of the edges.
4. The fiber preform according to claim 1, wherein the reinforcing
fibers of the reinforcing fiber bundles and/or the reinforcing yarn
strands of the at least one fiber tape are carbon fibers.
5. The fiber preform according to claim 1, wherein the at least one
first zone inside of the wall forms a continuous region formed from
reinforcing fiber bundles and the wall comprises at least one
discrete second zone arranged in and/or on the continuous region
made from reinforcing fiber bundles.
6. The fiber preform according to claim 1, wherein each reinforcing
fiber bundle has a length in the range from 10 to 50 mm.
7. A The fiber preform according to claim 1, wherein the wall has a
plurality of groups of reinforcing fiber bundles having lengths
different from each other.
8. The fiber preform according to claim 1, wherein each reinforcing
fiber bundle has 500 to 24,000 reinforcing fiber filaments.
9. The fiber preform according to claim 1, wherein the wall has
different groups of reinforcing fiber bundles having different
numbers of reinforcement fiber filaments from each other.
10. The fiber preform according to claim 1, wherein the wall in the
at least one first zone has a proportion of reinforcing fibers of
at least 45 vol. %.
11. The fiber preform according to claim 1, wherein the reinforcing
fiber bundles contain the first resin composition in a
concentration in a range from 2 to 5 wt. % in relation to the fiber
proportion.
12. The fiber preform according to claim 1, wherein the at least
one fiber tape comprises a plurality of reinforcing fiber strands
arranged next to each other.
13. The fiber preform according to claim 1, wherein the at least
one fiber tape has a length of at least 7 cm.
14. The fiber preform according to claim 1, wherein the at least
one fiber tape has the second resin composition in a concentration
from 1 to 10 wt. % in relation to the fiber proportion.
15. The fiber preform according to claim 1, wherein the first resin
composition and the second resin composition are identical.
16. A composite component produced from a fiber preform according
to claim 1.
17. A composite component, comprising: a wall constructed from
reinforcing fibers embedded in a polymer matrix, wherein: wherein
the wall has a first surface, a second surface lying opposite the
first surface and a thickness extending between the surfaces, and
is limited by edges, wherein the wall comprises at least one first
zone made from reinforcing fiber bundles and at least one second
zone made from at least one fiber tape comprising at least one
unidirectionally directed reinforcing yarn strand, wherein the
reinforcing fiber bundles in the at least one first zone are
oriented in differing spatial directions from each other when
viewed in a direction parallel to the thickness extension, wherein
each reinforcing fiber bundle comprises reinforcing fiber filaments
directed parallel to each other and has a length in the a range
from 3 to 50 mm, wherein the wall of the fiber preform has a
proportion of reinforcing fibers of greater than 35 vol. %, and
wherein the at least one second zone forms a discrete region when
viewed in a direction perpendicular to the thickness extension of
the wall and at least one fiber tape ends with at least one end
thereof inside of the wall.
Description
[0001] The present invention relates to a fiber preform for
producing fiber composite structures or composite components, the
wall thereof being made of reinforcing fibers, as well as to a
composite component made from this type of fiber preform.
[0002] Components made from fiber composite materials are
increasingly used, especially in the aerospace industrial sectors,
yet also e.g. in machine building industry. Fiber composites often
offer the advantage of lower weight and/or higher strength over
metals. An essential aspect thereby is the inexpensive production
of this type of resilient and yet light-weight composite components
at the same time. In view of the resilience, i.e. the rigidity and
strength, the volume percent of the reinforcing fibers and
especially also the direction of the reinforcing fibers have a
determining effect on composite components.
[0003] A commonly used manufacturing method is currently based on
the so-called prepreg technology. In this case, the reinforcing
fibers, such as glass fibers or carbon fibers, are arranged for
example parallel to one another, embedded in a matrix resin, and
processed into sheet-like semi-finished products. For component
manufacture, these sheets are cut according to the component
contour and laminated into a tool by machine or by hand
layer-by-layer while taking into account the orientation of the
reinforcing fibers as required by the component load. Subsequently,
the matrix is cured under pressure and at temperature in an
autoclave. This type of manufacturing process is, however, very
complex and expensive for many components.
[0004] In a further method, so-called fiber preforms are produced
from reinforcing fibers. Essentially, these are textile
semi-finished products in the shape of two- or three-dimensional
configurations made from reinforcing fibers, in which, in further
steps for producing the fiber composite component, a suitable
matrix material is introduced via infusion or injection, also by
application of vacuum. Subsequently, the matrix material is cured
at, as a rule, increased temperatures and pressures into the
finished component. Known methods for infusion or injection of the
matrix material in this case are the so-called liquid molding (LM)
method, or methods related thereto such as resin transfer molding
(RTM), vacuum assisted resin transfer molding (VARTM), resin film
infusion (RFI), liquid resin infusion (LRI), or resin infusion
flexible tooling (RIFT).The fiber material used to produce the
fiber preforms can also already be impregnated e.g. with low
amounts of a curable plastic material, i.e. a binder material, in
order to improve the fixing of the reinforcing fibers in the fiber
preform. Pre-impregnated yarns of this type are described for
example in WO 2005/095080.
[0005] In order to produce such fiber preforms, WO 98/22644 has
already suggested dispersing short-cut reinforcing fibers together
with a binder material on an air-permeable screen adapted to the
shape of the desired fiber preform and maintaining said fibers on
the screen through the application of vacuum until, after cooling
of the binder material, a sufficient stability of the preform is
achieved. By means of this procedure, the reinforcing fibers are
arranged in random, isotropic arrangements and directions. This is
indeed advantageous if the load directions in the component cannot
be predicted in advance; however, it has the simultaneous
disadvantage that, due to the isotropic orientation, only a
fraction of the fibers lie in the load direction. An adaptation to
special load directions in the component is thus not possible when
using this method. Reinforcements in the component wall can, at
most, be made via e.g. locally increased wall thicknesses; however
they are associated with an increase in weight of the component. In
addition, according to the examples of WO 98/22644, only fiber
volume proportions in the range of up to approximately 15 vol. %
are achieved, and therefore, due to the low fiber volume
proportions, only comparably low thickness-related component
strengths. Usually, fiber proportions of a maximum of 30 vol. % are
achieved for components of this type having random orientation of
the reinforcing fibers.
[0006] In US 2010/0126652 A1 and US 2009/0229761 A1, a method and a
device, respectively, for producing fiber preforms are described,
by means of which it is possible to satisfy the demand for a
load-appropriate fiber direction in the component. In this case, a
so-called TFP method ("tailored fiber placement method") is used,
in which yarns or fiber strands are laid along any number of paths
adapted to the distribution of forces affecting the finished
component and pre-fixed using fixing threads, wherein CNC
controlled sewing and knitting machines are used therefor. US
2009/0229760 A1 describes an application device for the fiber
strands suitable for a TFP method of this type. Using these TFP
methods, an improved utilization of the mechanical resistance of
the reinforcing fibers and an increased adaptation of the component
cross sections to the respective local loads in the component are
possible. However, these methods, in particular in the production
of fiber preforms with complex, three dimensional structures, are
complex and cost intensive.
[0007] As an alternative to fixing the fiber strands by means of a
textile method, such as by means of sewing or knitting methods, the
fiber strands can also be fixed by means of a thermally activated
binder material, for example by means of a thermoplastic, as is
described in DE 10 2007 012 608 B4.
[0008] A further possibility for the production of fiber preforms
consists in the use of so-called multiaxial non-crimp fabrics.
Multiaxial non-crimp fabrics are understood to be structures made
from a plurality of superimposed fiber layers, wherein the fiber
layers comprise sheets of reinforcing yarns arranged parallel to
each another. The superimposed fiber layers can be connected and
secured to each other via a plurality of sewing or knitting threads
arranged side-by-side and running parallel to each other and
forming stitches, such that the multiaxial non-crimp fabrics is
stabilized in this way. The fiber layers are superimposed such that
the reinforcing fibers of the layers are directed parallel to each
other or alternately crosswise (e.g. -45.degree.; 0.degree.,
+45.degree..
[0009] Multiaxial non-crimp fabrics of this type are laid without
matrix material in a mold and e.g. for shaping are adapted to its
contours using increased temperature. Subsequently, the matrix
material required for the production of the composite component is
introduced into the mold and into the fiber preform via infusion or
injection, whereby, following curing of the matrix material, the
composite component is obtained. Multiaxial non-crimp fabrics and
the use thereof to produce fiber preforms are described for example
in EP 0 361 796 B1, EP 1 352 118 B1, or WO 98/10128.
[0010] Multiaxial non-crimp fabrics are, however, expensive to
produce, and are generally produced in standard widths, which
seldom correspond to the dimensions of the later component. This
results in a not insignificant amount of waste. In addition,
especially in components with complex contours and particularly
with respect to components with small radii of curvature, they can
only be used to a limited extent, as the multiaxial non-crimp
fabrics cannot be draped into any form. Further, it was observed
that the sewing or knitting threads can often lead to a reduction
in the impact strength of the resulting composite. Finally, the
later infusion or injection of the matrix material can also be
slowed down over the liquid molding or related methods.
[0011] To avoid seams and transverse filaments, US 2008/0085650 A1
suggests using reinforcing material structures having a layered
construction, said reinforcing material structures comprising a
layer of continuous reinforcing fibers directed in parallel as well
as a layer made from e.g. a non-woven, a woven fabric, or from
short cut fibers, wherein the layers are connected to each other
via an adhesive or via adhesive points. These materials are also
initially available in standard widths, which have to be cut
corresponding to the component geometry. In this way, increased
costs occur due to additional steps, for example cutting, draping,
and connecting, as well as an average waste of up to 30% of the
output material.
[0012] It is the object of the present invention to provide a fiber
preform which can find use in a plurality of component contours, in
which in particular an improved adaptation to the respective local
loads in the component is possible, and which can be inexpensively
produced.
[0013] The object is achieved by a fiber preform for producing
fiber composite structures, the wall thereof being made from
reinforcing fibers, [0014] wherein the wall has a first surface, a
second surface lying opposite the first surface and a thickness
extending between the surfaces, and is limited by edges, [0015]
wherein the wall comprises at least one first zone made from
reinforcing fiber bundles having a first resin composition and at
least one second zone made from at least one fiber tape comprising
at least one unidirectionally directed reinforcing yarn strand
having a second resin composition, wherein the reinforcing fiber
bundles in the at least one first zone are oriented in differing
spatial directions from each other when viewed in a direction
parallel to the thickness extension, [0016] wherein each
reinforcing fiber bundle comprises reinforcing fiber filaments
directed parallel to each other, has a length in the range from 3
to 50 mm, and contains the first resin composition in a
concentration in the range from 1 to 10 wt. % relative to the fiber
weight, wherein the wall of the fiber preform has a proportion of
reinforcing fibers of greater than 35 vol. %, and [0017] wherein
the at least one second zone forms a discrete region when viewed in
a direction perpendicular to the thickness extension of the wall
and at least one fiber tape ends with at least one end thereof
inside of the wall.
[0018] By means of the fiber preform according to the invention, a
fiber composite structure or a composite component can be produced
in a simple way. In this case, the fiber preform according to the
invention can be laid in a near-net-shape mold by means of common
methods, a matrix material is introduced into the mold and thus
into the fiber preform via infusion, infiltration, or injection,
and subsequently the composite component is formed by curing the
matrix material. The invention therefore also relates to a
composite component, the wall thereof being constructed from
reinforcing fibers embedded in a polymer matrix, [0019] wherein the
wall has a first surface, a second surface lying opposite the first
surface and a thickness extending between the surfaces, and is
limited by edges, [0020] wherein the wall comprises at least one
first zone made from reinforcing fiber bundles and at least one
second zone made from at least one fiber tape comprising at least
one unidirectionally directed reinforcing yarn strand, [0021]
wherein the reinforcing fiber bundles in the at least one first
zone are oriented in differing spatial directions from each other
when viewed in a direction parallel to the thickness extension,
[0022] wherein each reinforcing fiber bundle comprises reinforcing
fiber filaments directed parallel to each other and has a length in
the range from 3 to 50 mm, [0023] wherein the wall of the fiber
preform has a proportion of reinforcing fibers of greater than 35
vol. %, and [0024] wherein the at least one second zone forms a
discrete region when viewed in a direction perpendicular to the
thickness extension of the wall and at least one fiber tape ends
with at least one end thereof inside of the wall.
[0025] The fiber preform or the composite component has thus inside
of the wall thereof at least one first zone made from reinforcing
fiber bundles and at least one second zone made from at least one
fiber tape. In this case, the first zone inside of the wall can
form a continuous region over the entire wall, in which e.g. one or
more second zones are embedded. The second zones can thereby be
arranged inside of the wall, i.e. forming islands when viewed
perpendicular to the thickness extension of the wall. The second
zones can, however, in a preferred embodiment, also be arranged in
the region of one of the surfaces on the first zone, i.e. in this
case at least one fiber tape is mounted, for example, on one of the
surfaces. It is, however, also possible that a second zone extends
over the entire wall thickness and is thereby laterally limited by
first zones. In each case, the at least one second zone forms a
discrete region when viewed in a direction perpendicular to the
thickness extension of the wall, i.e. the at least one second zone
does not form a continuous region over the entire wall when viewed
in this direction. As previously explained, only the at least one
first zone can extend over the entire wall as a continuous region.
In a preferred embodiment of the fiber preform according to the
invention, the at least one first zone inside of the wall forms,
over the entire wall, a continuous region made from reinforcing
fiber bundles and the wall comprises at least one discrete second
zone arranged in and/or on the continuous region made from
reinforcing fiber bundles.
[0026] In the at least one first zone, the reinforcing fiber
bundles are oriented in different spatial directions from each
other when viewed in a direction parallel to the thickness
extension, i.e. the reinforcing fibers are distributed or oriented
isotropically in the at least one first zone in the spatial
directions perpendicular to the thickness extension. Isotropically
is thereby understood as meaning that, while there is an
anisotropic orientation of the fibers within the individual
reinforcing fiber bundles, the bundles in their totality show no
preferred orientation but are isotropically oriented in the cited
spatial directions. In particular with regard to thicker walls or
thicker layer thicknesses of the first zones, there can also be an
isotropic distribution taking into account the spatial direction
extending in the direction of the thickness of the wall, i.e. the
fiber preform or the composite component can have an isotropic
structure in all three spatial directions in the at least one first
zone.
[0027] According to the invention, each reinforcing fiber bundle
comprises reinforcing fiber filaments directed parallel to each
other and has a length in the range from 3 to 50 mm. Preferably,
the length lies in the range from 10 to 50 mm. In view of the
attainable proportions of reinforcing fibers in the at least one
first zone, in particular for achieving proportions above 40 vol.
%, it is advantageous if the wall of the fiber preform or of the
composite component according to the invention has a plurality of
groups of reinforcing fiber bundles having differing lengths in the
at least one first zone, such that overall the lengths of the
reinforcing fiber bundles have a distribution. For example,
reinforcing fiber bundles having a length of 20, 30, and 50 mm can
be or are combined with each other.
[0028] The reinforcing fiber bundles can comprise common filament
yarns having e.g. 500 to 50,000 reinforcing fiber filaments. It is,
however, advantageous if each reinforcing fiber bundle comprises
500 to 24,000 reinforcing fiber filaments. To achieve a most
homogeneous distribution of the reinforcing fiber bundles in the at
least one first zone, and to achieve the highest possible fiber
proportions, the number of reinforcing fiber filaments in the
reinforcing fiber bundles lies particularly preferably in the range
from 500 to 6,000 and more particularly preferably in the range
from 1,000 to 3,000.
[0029] To achieve high fiber volume proportions in the at least one
first zone, in particular to achieve proportions of reinforcing
fibers above 40 vol. %, it has likewise proven to be advantageous
if the wall has a plurality of groups of reinforcing fiber bundles
having differing numbers of reinforcing fiber filaments, because
this allows the realization of high packing densities of the
bundles in the at least one first zone. For example, reinforcing
fiber bundles having 3,000, 6,000, and 12,000 reinforcing fiber
filaments can be combined.
[0030] To achieve high packing densities of the bundles, i.e. to
achieve high fiber volume proportions in the at least one first
zone of more than 40 vol. %, it is further advantageous if the
reinforcing fiber bundles have a cross section that is as flat as
possible perpendicular to the extension of the reinforcing fiber
filaments in the bundle. Preferably, the reinforcing fiber bundles
are strip shaped and have a ratio of bundle width to bundle
thickness of at least 25. Particularly preferably, the ratio of
bundle width to bundle thickness lies in the range of 30 to
150.
[0031] Through suitable selection of reinforcing fiber bundles with
respect to the ratio of bundle width to bundle thickness, with
respect to the length, as well as with respect to the number of
reinforcing fiber filaments, especially high packing densities of
the reinforcing fiber bundles and thus especially high fiber volume
proportions can be realized in the at least one first zone. In a
more particularly preferred embodiment of the fiber preform or the
composite component, the reinforcing fiber bundles arranged in the
region of the at least one first zone in the wall of the fiber
preform or of the composite component have, in addition to a flat
cross section, differing lengths and differing numbers of
reinforcing fiber filaments. This leads to especially high fiber
volume proportions in the wall of the preform or component.
According to the invention, the wall of the fiber preform or of the
composite component has across its entire extension, i.e. at every
point of its extension, a proportion of reinforcing fibers of at
least 35 vol. %, preferably a proportion of reinforcing fibers of
at least 40 vol. %, and particularly preferably of 45 vol. %. It is
especially advantageous if the proportion of reinforcing fibers
amounts to at least 50 vol. % because this leads to superb
mechanical properties in the composite component. The
pre-impregnation of the reinforcing fiber bundles with the first
resin composition thereby allows for a compact, stable laying of
these reinforcing fiber bundles during the production of the fiber
preform, by which means the realization of such high fiber volume
proportions is supported.
[0032] The proportion of reinforcing fibers in the wall of the
fiber preform can be determined following DIN EN 2564:1998. For
this purpose, the fiber preform is impregnated according to usual
methods with an epoxy resin such as HexFlow RTM 6 (Hexcel) and
cured into a composite material. Test bodies are cut from the cured
composite material, from which mass and density are determined
according to DIN EN 2564:1998, as well as, after treatment with
concentrated sulfuric acid to separate the matrix resin, the mass
of the fibers contained in the test bodies.
[0033] According to the provisions of DIN EN 2564:1998, the fiber
mass proportion can thus be determined and, resulting therefrom,
the fiber volume proportion or the proportion of reinforcing
fibers. This method can also be used to determine the fiber volume
proportion for the composite components.
[0034] The reinforcing fiber bundles in the fiber preform have
inventively a content of a first resin component in the range of 1
to 10 wt. % in relation to the fiber proportion. By this means, a
sufficient stability is provided to the fiber bundles and a
disintegration into individual filaments or individual groups of
filaments is avoided. At the same time, use of the resin
applications according to the invention guarantees that the
reinforcing fiber bundles adhere to each other during the formation
of the fiber preform and the fiber preform thus achieves a
sufficient stability for additional handling. A resin application
of this type is often designated as a binder or as a binding. As
has already been explained, the actual matrix material still
required for the formation of the composite component is introduced
in a later process step by infusion or injection into the preform.
Preferably, the reinforcing fiber bundles in the fiber preform
contain the first resin composition in a concentration in the range
from 2 to 7 wt. % in relation to the fiber proportion.
[0035] With regard to the first resin composition, this can be
binder material that fulfills the above-mentioned object. In a
preferred embodiment of the invention, the first resin composition
is a thermally activatable binder material, for example a
thermoplastic. However, preferably the binder material is based on
epoxy resins, wherein the binder material can be multiply melted
and can be converted to a fixed state by cooling to room
temperature. Resin compositions of this type, or reinforcing fibers
that have these types of resin compositions, are disclosed for
example in WO 2005/095080. WO 98/22644 also discloses these types
of resin compositions suitable as binders.
[0036] The at least one fiber tape on or inside of the at least one
first zone and thus the at least one second zone itself is arranged
e.g. in regions of especially high strain in the subsequent
component produced from the fiber preform or in the composite
component according to the invention and is correspondingly
oriented to the stress directions prevailing there. The at least
one fiber tape is thus preferably arranged in orientation with the
forces or directed in accordance with the load in the wall of the
fiber preform or of the composite component. Thereby, the at least
one fiber tape or the fiber tapes can extend from one side or edge
of the wall of the fiber preform or of the composite component to
another side or edge of the fiber preform or of the composite
component and thus over the entire extension in this region. The
edges can thereby define the outer perimeter of the fiber preform;
however they can also appear in the inside of the fiber preform by
means of recesses, openings, projections, among others.
[0037] The fiber preform according to the invention distinguishes
itself especially in that it can be flexibly adapted to local loads
in the component to be produced from the fiber preform. Therefore,
the fiber preform has in one embodiment at least one fiber tape
which ends with at least one of the ends thereof inside the wall,
and said fiber tape thus does not extend from one edge of the fiber
preform to another edge. A fiber tape or a plurality of fiber tapes
thus extend only over parts of the respective expansion or
extension of the wall in the direction of this one fiber tape, or
these fiber tapes, thus forming island-shaped or peninsula-shaped
regions. The ends of a fiber tape thereby correspond to the ends of
at least one unidirectionally directed reinforcing yarn strand
forming this fiber tape. For example, it is also possible, in the
case that a fiber preform or a composite component has a projection
for forming a fitting, that fiber tapes are applied as
reinforcement only in the region of the projection. The fiber tapes
or at least one fiber tape can thereby also be applied or run in a
curved path.
[0038] Preferably the at least one fiber tape has a length of at
least 7 cm and especially preferably of at least 10 cm. At shorter
lengths, the force transmission into the fiber tapes in a component
is insufficient. In addition, the handling of shorter fiber tapes,
in particular in automated laying, as is described for example in
DE 10 2007 012 608 B4, is difficult. The at least one fiber tape
has especially preferably a length of at least 20 cm. As previously
explained, an upper limit of the fiber tape length results from the
component geometry in individual cases.
[0039] The at least one fiber tape can e.g. comprise one single
multifil reinforcing yarn that is spread and laid flat, i.e. one
single reinforcing yarn strand. Preferably, however, the at least
one fiber tape comprises a plurality of reinforcing yarn strands
arranged side-by-side and parallel to each other.
[0040] In an embodiment of the fiber preform according to the
invention or the composite component, the at least one second zone
can thereby comprise one individual fiber tape, which can also
comprise a plurality of multifil reinforcing yarns applied next to
and over each other. Preferably, however, the at least one second
zone comprises a plurality of fiber tapes arranged in layers over
each other, wherein the number of the layers as well as their width
results from the respective loads in the subsequent component.
[0041] As explained, due to the specific construction of the fiber
preform according to the invention, a load-appropriate construction
of the fiber preform as well as of the components produced
therefrom is possible in a simple way. This is achieved herein in
that the at least one fiber tape is preferably arranged in the wall
of the fiber preform or of the composite component in orientation
with the forces, or directed in a load-appropriate way. In one
embodiment, therefore, the wall of the fiber preform or of the
composite component comprises at least two fiber tapes and the
orientation of the at least one unidirectionally directed
reinforcing yarn strand of at least one fiber tape is different
from the orientation of the at least one unidirectionally directed
reinforcing yarn strand of another fiber tape. In one embodiment,
inside of a second zone, fiber tapes which are arranged in layers
over each other, or the unidirectionally directed reinforcing yarn
strands within and forming said fiber tapes, can thereby have
different orientations. In a further embodiment, in the case of a
plurality of second zones on and/or in the wall of the fiber
preform or of the composite component, fiber tapes of different
second zones, or the unidirectionally directed reinforcing yarn
strands of different second zones within and forming the fiber
tapes, can have different orientations. The differently oriented
reinforcing yarn strands can form for example an angle a in the
range of 5.degree. to 175.degree., and preferably 20.degree. to
160.degree. to each other. This naturally also comprises
embodiments in which fiber tapes inside of one second zone and
those of different second zones have differing orientations to each
other.
[0042] In a further preferred embodiment, at least one
unidirectionally directed reinforcing yarn strand of at least one
fiber tape, or at least one fiber tape, in respect to the
longitudinal extension thereof, is not directed parallel to any of
the edges of the fiber preform or of the composite component.
[0043] According to the invention, the unidirectionally directed
reinforcing yarn strands or the at least one fiber tape have a
second resin composition. By this means, a secure laying and fixing
of the at least one fiber tape is enabled and a stabilization of
the fiber preform is achieved. Depending on the application, the
fiber tape can be a so-called unidirectional prepreg, in which the
unidirectionally oriented reinforcing fibers are already
impregnated with matrix resin and the concentration of the matrix
resin in the prepreg already substantially corresponds to the
concentration in the component, i.e. in the range from
approximately 25 to 45 wt. %. Preferably, however, the at least one
fiber tape of the fiber preform according to the invention has the
second resin composition in a concentration of 1 to 10 wt. %
relative to the fiber proportion. The second resin composition then
functions likewise as a binder material. At concentrations of this
type, the previously mentioned good handling and fixing are
guaranteed on the one hand. On the other hand, the at least one
fiber tape has a sufficient flexibility and there is a good
infiltration with the matrix resin during the subsequent component
processing.
[0044] The proportion of reinforcing fibers in the at least one
fiber tape of the at least one second zone of the fiber preform
should be lower than 70 vol. % so that in the finished component
after the infiltration with matrix resin a substantially complete
embedding of the reinforcing fibers in the matrix resin is
guaranteed. On the other hand, the proportion of fibers should be
as high as possible so that a highest possible reinforcing effect
is achieved at the given volume. Not least, but also under
consideration of the practical handleability, the volume
proportions of reinforcing fibers in the at least one fiber tape of
the fiber preform or of the composite component have been shown to
be suitable in the range from 40 to 65 vol. % and preferably in the
range from 50 to 65 vol. %.
[0045] With regard to the second resin composition, it can, like
the first resin composition, be a thermally activatable binder
material, for example, a thermoplastic. A binder material based on
epoxy resins is likewise preferred, wherein the binder material can
be multiply melted and can be converted to a fixed state by cooling
to room temperature. Also, with regard to the second resin
composition or with regard to the fiber tapes which have these
resin compositions, the yarns and resin compositions disclosed for
example in WO 2005/095080 can be considered. Preferably, the first
resin composition and the second resin composition are chemically
similar and especially preferably identical. Suitable resin
compositions or binder materials are also described e.g. in the
already mentioned WO 98/22644.
[0046] With regard to the reinforcing fibers or reinforcing fiber
yarns used in the fiber preform according to the invention or the
composite component according to the invention, said fibers or
yarns can be those based on carbon, glass, aramid, ceramics, boron,
steel or on synthetic polymers like polyamide, polyhydroxy ether,
polyethylene, in particular UHMW polyethylene, or polyester, or a
combination of these materials, for example in the form of mixed
yarns (co-mingled yarns). In a preferred embodiment, the
reinforcing fibers of the reinforcing fiber bundles and/or the
reinforcing yarn strands of the at least one fiber tape are carbon
fibers. In this case, the carbon fibers can be those that are
obtained from pitch, polyacrylonitrile or viscose pre-products.
[0047] The combination of isotropically directed reinforcing fiber
bundles and fiber tapes or reinforcing yarn strands directed in
orientation with the forces allows for an inexpensive production of
fiber preforms, which production can simultaneously be adapted to
the specific loads in the subsequent component. Thus, the first
zones can be inexpensively formed with reinforcing fiber bundles
e.g. via so-called fiber spraying processes, in which reinforcing
fiber yarns applied with the first resin composition are fed to a
cutting head, cut to correspondingly measured bundles having the
desired length, and finally sprayed into a tool adapted to the
final contours of the fiber preform. Alternatively, a fill made of
corresponding reinforcing fiber bundles can also be deposited in
the tool. In both cases, the positioning of the reinforcing fiber
bundles can be supported through the application of vacuum to the
tool, which is perforated in this case.
[0048] At the same time, or also e.g. subsequently, in regions in
which there will be increased load in the subsequent component,
fiber tapes can be applied oriented in the direction of the loads,
wherein for this purpose known methods from the prior art can be
used, like the application method disclosed in WO 2007/101578 using
a flame spraying method to deposit the second resin composition
during the application, or the method disclosed in DE 10 2007 012
608 B4 in which the fiber tapes or the reinforcing fiber strands,
which are provided with a thermally activatable binder material,
for example with a thermoplastic, thus a second resin composition,
are positioned by means of an automated application device over a
laying head. Methods of this type are also known under the
designation "fiber placement methods".
[0049] In this way, in contrast to the fiber preforms of the prior
art, fiber preforms having in principle any possible flat or
two-dimensional surface geometry, or preferably having a
three-dimensional surface geometry diverging from the flat surface
geometry, can be produced by means of the present invention. The
preform according to the invention and also the composite component
according to the invention can have different wall thicknesses over
the extension of the wall thereof or also projections, openings,
etc. A preferred fiber preform therefore has in particular
different wall thicknesses in the region of the at least one first
zone.
[0050] By this means the fiber preform according to the invention
or the composite component according to the invention can be
available in a plurality of different embodiments. By flexibly
controlling the first and second zones in relation to each other, a
simple adaptation to the loads in the component can be obtained.
Thus, according to load locations, an adaptation can be effected
through increasing the wall thickness via additional proportions of
first zones, i.e. by adding reinforcing bundles. Likewise, a
reinforcement is possible in specific regions via second zones
having fiber tapes oriented in the direction of load. By this
means, depending on the specific component or depending on the
specific fiber preform, the proportion of first zones having
reinforcing fiber bundles can outweigh the proportion of second
zones having fiber tapes made of reinforcing yarn strands, or vice
versa. Key to determining the embodiment in this case are the
predicted loads in the final component as well as the goals to be
achieved with respect to e.g. wall thicknesses, weight, volume,
etc. and not the least also with respect to the manufacturing costs
of the component.
[0051] The invention will now be described in more detail by way of
the following figures, wherein the figures shall have no limiting
character. In simplified schematic representation:
[0052] FIG. 1 shows a top view of an fiber preform according to the
invention in the shape of a curved calotte segment.
[0053] FIG. 2 shows a cross-section through the fiber preform
segment shown in FIG. 1 along the line A-A.
[0054] FIG. 1 schematically shows a fiber preform 1 in the shape of
a curved calotte segment having a first surface 2 and a second
surface 3 and a thickness extending between the surfaces. From a
top view of the first surface 2, the first zones 4 made from
reinforcing fiber bundles 5 can be recognized, said bundles being,
on average, isotropically oriented in different directions. The
reinforcing fiber bundles 5 are constructed from short-cut
reinforcing filaments 6 that run parallel to each other, wherein
the number of reinforcing fiber filaments in the bundle can lie in
the range from 500 to 50,000. The reinforcing fiber bundles 5 are
provided with a first resin composition by which means a good
adhesion of the reinforcing fiber bundles to each other is achieved
and the fiber preform obtains sufficient stability for further
handling.
[0055] In the present example, the fiber preform 1 has two second
zones 7a, 7b on its first surface 2 in the form of fiber tapes that
comprise unidirectionally directed reinforcing yarn strands 8a, 8b.
In the example shown, the second zone 7a extends over the surface 2
from one edge to the opposing edge, while the second zone 7b only
runs over a segment of the surface and ends inside of the wall. The
reinforcing yarn strands 8a, 8b of the second zones 7a, 7b are
oriented in different directions and are not directed parallel to
any of the edges of the fiber preform.
[0056] FIG. 2 shows a cross-section through the fiber preform
segment schematically represented in FIG. 1. Therefore, the same
parts are provided with the same reference numbers. The fiber
preform 1 is present as a curved segment having a first surface 2
and a second surface 3, between which extends the thickness of the
wall of the fiber preform. The wall is constructed from a first
zone 4 and second zones 7a, 7b, 9, 10, wherein in the
cross-sectional representation it is clear that the first zone 4
forms, over the entire wall, a continuous region made from
reinforcing fiber bundles 5 and said zone can be designated as a
continuous phase. In contrast, the second zones 7a, 7b, 9, 10 are
embedded as discrete regions in the first zone 4. In FIG. 2, in
addition to the zones 7a, 7b shown in
[0057] FIG. 1 on the first surface 2, two additional second zones
9, 10 are represented in the wall interior, which zones are
completely surrounded by the first zone 4. The second zones 7a, 7b,
9, 10 are constructed from reinforcing yarn strands 8, 8a, 8b which
are arranged over each other in several layers.
[0058] The fiber preform shown in FIGS. 1 and 2 has a relatively
large thickness. Therefore, in this example, the reinforcing fiber
bundles 5 are also oriented substantially isotropically over the
wall cross-section in the cross-sectional view.
* * * * *